Bolt holes 23 are provided for press fitting and securing bolts 5 for mounting a brake rotor 4 to a flange 22 of a hub wheel. Each bolt hole 23 includes widening portions 28a, 28b, which are tapered to widen from the center portion of the bolt hole 23 toward a brake rotor mounting surface 25 of the flange 22. The widening portions 28a, 28b are formed by two tapered surfaces having different taper angles with respect to the axis of the bolt hole 23 from an opening rim of the bolt hole toward the inside. The taper angle of an outer tapered surface connected to the opening rim is greater than the taper angle of an inner tapered surface connected to the outer tapered surface. In machining the hub wheel 2 configured as described above, the brake rotor mounting surface 25 is finished after machining the bolt holes 23.